Experimental demonstration of charge inversion in a protein channel in the presence of monovalent cations

Charge inversion takes place when interfacial charges attract counterions in excess of their own nominal charge. To date, this phenomenon has been reported in a variety of membrane channel systems in the presence of multivalent cations. Here, we investigate the charge inversion phenomenon in a protein channel in solutions of monovalent cations. To this end, we perform selectivity experiments in salts of different cations, changing both the electrolyte concentration and the solution acidity. We show that charge inversion can be produced by two different mechanisms, namely specific adsorption and competitive binding. (C) 2014 Elsevier B.V. All rights reserved.